adds output nml used to trigger yaco pressure level output

examples/DestinE_output_nml.txt

+&output_nml ! ATM-YACO comms for pressure levels
+    output_filename  = "pressure_levels"
+    filetype         = 999
+    !operation        = 'mean'
+    output_grid      = .FALSE.
+    output_start     = "${start_date}"
+    output_end       = "${end_date}"
+    output_interval  = "${atmTimeStep}"
+    steps_per_file   = 0
+    pl_varlist       = 'clw', 'gpsm', 'hur', 'hus', 'omega', 'pv', 'ta', 'ua', 'va'
+    p_levels         = ${pressure_levels}
+    remap            = 0
+/